Pressure safety assembly for heat exchangers



Feb. 14, 1961 BELL 2,971,746

PRESSURE SAFETY ASSEMBLY FOR HEAT EXCHANGERS Filed Aug. 27, 1957 PRESSUR/ZER INVENTOR ALA/V 5541.

ATTORNEY heat exchanger.

PRESSURE SAFETY ASSEMBLY FOR HEAT EXCHANGER Alan Bell, ookham, England, assignor to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Aug. 27, 1957, Ser. No. 680,516

6 fiiaims. (Cl. 257-1) This invention relates to heat exchange apparatus and more particularly pertains to an improved pressure safety assembly for a heat exchange apparatus wherein two fluids are passed in indirect heat exchange relationship and where one of the fluids is maintained under a lower pressure than the other fluid by a gas or vapor supplied to the vapor space of an expansion tank or pressurizer disposed in the low pressure fluid circuit.

In heat exchange apparatus wherein a liquid or vaporliquid mixture, as for example, liquid sodium, is passed in indirect heat exchange relationship in a heat exchanger with a fluid, as for example, water and/or steam which is at a pressure greater than the liquid or vapor-liquid mixture, the pressurizer is usually provided with a pressure relief device for relieving the low pressure liquid circuit at a predetermined maximum safe pressure which the low pressure circuit is constructed to safely withstand. However, in such apparatus, in the event of failure of the partition or wall separating the two fluids, as for example, the tube walls in a tube and shell type of heat exchanger, the inrush of high pressure fluid into the relatively incompressible low pressure liquid may cause a local rise in pressure above the maximum safe pressure before the pressure relief device at the pressurizer becomes effective to relieve the pressure. This local rise in pressure is (inagerous in that it may cause serious damage to the appartus and possible uncontrolled escape of liquid out of the system into the air, escape of liquid being particularly dangerous where the leakage is molten sodium which violently reacts with air.

Accordingly, it is an object of the present invention to provide in apparatus, as aforedescribed, a pressure safety assembly'wherein the possibility of a pressure rise above a predetermined safe value in the low pressure fluid circuit is obviated.

The present invention, therefore, contemplates a novel pressure safety assembly for a heat exchange apparatus in which two fluids are passed in indirect heat exchange relationship in a heat exchanger and where one of the fluids is maintained at a lower working pressure than the other fluid by a gas or vapor supplied to an expansion tank or pressurizer. The pressure safety assembly according to this invention comprises an unobstructed conduit which communicates at one end with the vapor space of the pressurizer to receive gas or vapor from the latter and at the opposite end communicates with the interior of the heat exchanger to receive low pressure fluid. A pressure relief device is disposed in the conduit near the The pressure relief device is operative to release low pressure fluid through the conduit when the pressure in the low pressure fluid exceeds a predetermined maximum safe pressure, which pressure the low pressure side of the heat exchange apparatus is constructed to withstand.

The invention will be understood from the following description when considered in connection with the accompanying drawing:

In the drawing, the pressure safety assembly 10, accord- 2,971,746 i 'atented Fete. 14, 1961 ing to this invention, is shown as applied to a nuclear reactor steam generating apparatus 11, which apparatus is shown somewhat diagrammatically. Steam generating apparatus 11 comprises essentially a nuclear reactor 12 and a heat exchanger 13. Fluid, such as molten sodium, is heated in reactor 12 and is passed from reactor 12 by way of line 14 and a circulation pump 15 to heat exchanger 13. Heat exchanger 13 which may be of the shell and tube type has a plurality of tubes 16. Tubes 16 are connected to receive a fluid to be heated, such as water, which water in flowing through tubes 16 of heat exchanger 13 passes in indirect heat exchange relationship with the heated molten sodium and is thereby heated and vaporized or partly vaporized. The molten sodium, which is cooled in passing in heat exchange relationship with the water, flows from heat exchanger 13 via line 17 to reactor 12 where it is again heated. An expansion tank or pressurizer 18, having a vapor space 19 and a liquid space 20, is connected to receive molten sodium in liquid space 20 through connection 21 which communicates at one end with vapor space 19 and at the opposite end with line 17. A gas or vapor, as for example, argon, neon, nitrogen or other suitable fluid, which is inert with respect to the molten sodium, is supplied to vapor space 19 of pressurizer 18 from a suitable source (not shown), through a valved line 22. The gas is supplied to pressurizer 18 at a pressure above atmospheric pressure, and the gas in the pressurizer maintains the molten sodium, circulating through reactor 12 and heat exchanger 13, under a relatively low work pressure. The water flowing through tubes 16 of heat exchanger 13 is at a pressure substantially higher than the pressure of the molten sodium. A pressure relief device 23, herein illustrated as a spring loaded valve may be a rupturable diaphragm or any other suitable pressure relief device, is disposed in a conduit 42 which communicates at one end with vapor space 19 of pressurizer 18 and at the other end with the atmosphere. Pressure relief device 23 is constructed to open when the pressure rises in the liquid sodium circuit above a predetermined maximum safe pressure.

Pressure safety assembly 10 comprises an unobstructed conduit 25 which is connected at one end to the shell of heat exchanger 13 and is in communication with the molten sodium in heat exchanger 13. At the opposite end conduit 25 is connected to conduit 24 at a point between pressurizer 18 and pressure relief device 23 so as to be in communication with vapor space 19 of pressurizer 18. Conduit 25 may be connected to the pressurizer so as to directly communicate with the vapor space 19 of pressurizer 18. In conduit 25, a pressure relief device 26, such as a spring loaded valve assembly as illustrated, or a rupturable diaphragm, is disposed in close proximity to heat exchanger 13. Since one end of conduit 25 communicates with molten sodium in heat exchanger 13 and at the other end with vapor space 19 of pressurizer 18 to receive vapor or gas from the latter at substantially the working pressure of the molten sodium, the pressure on both sides of the valve 27 of pressure relief device 26 is substantially the same. With the pressures substantially equal on both sides of valve 27, leakage of molten sodium between valve 27 and its seat is eliminated. In addition, oxidation of valve 27 at the seat is obviated because conduit 25 is filled with a gas or vapor, inert with respect to molten sodium, thereby maintaining the molten sodium out of contact with air with which molten sodium reacts to cause rapid corrosion of surfaces adjacent the point of reaction. If pressure relief device 26 is a rupturable diaphragm disposed across the flow area of conduit 25, substantially equal pressures on either side thereof will minimize flexure and the consequent breaking of the diaphragm by action of fluctuation in the working'pressure of the molten sodium, thereby obviating premature failure of the diaphragm.

In operation of heat exchange apparatus 11, molten sodium is heatedin reactor 12 and is circulated by cir-v culation pump. into heat exchanger 13 via line" 14'. In heat exchanger 13," the molten sodiurrr'pas'ses' in'h'eat. exchange "relationship with water flowing through tubes 16 where at least some ofthe water is convertedto steam and the molten sodium is cooled. The steam. or steam and water mixture is passed from heat exchangerlS to a point of use (not'shown), as for example, a turbine. The cooled molten sodium passes from heat'exchanger 13, through line 17 to reactor 12' for reheating. The molten sodium is maintained under a relatively low work ing pressure, asfor example 40 p.s.i. gage by inert gas or vapor which is supplied to vapor space 19 of pressurizer 18 by way of valved line 22 from a'suitable source' (not shown) of that gas or vapor;

In order to'more clearly understand the operation of the invention, let it be assumed that the molten sodium side of heat exchange apparatus 11 is" constructed to withstand a maximum safe pressure of 130 p.s.i. gage and that the water in heat exchanger 13 is at a pressure above 130 p.s.i. gage. Under the aforesaid'values, pressure relief devices 23 and 26 are constructed to open (rupture in the case of a diaphragm) when the pressure differential across the pressure relief devices is 90 p.s.i. gage, that is, the difference between the maximum safe pressure of 130 p.s.i. gage and the working'pressure of 40 p.s.i. gage. If under'the aforesaid operating values, a sudden rise in pressure occurs in the molten sodium side or low pressure side of heat exchange apparatus 11 by reason of an inrush of high pressure Water and/or steam through a rupture or failure of one or more of tubes 16, such pressure rise will be quicklytransmitted through the molten sodium in conduit 25 to pressure relief device 26. Because pressure relief device 26 is disposed considerably closer to heat exchanger 13 than pressure relief device 23, pressure relief device 26 will open to release the excessive pressure of the molten sodium before relief device 23 is effective to release ex-' cess pressure and before the pressure builds up to apoint beyond the maximum safepressure of 130 p.s.i. gage at which structural damage to the heat exchanger 13 might occur. The release of molten sodium through conduit 25 causes an increase in pressure on the pres surizer side-of pressure relief device 23 thereby causing pressure relief device 23 to open (rupture if device 23 is a rupturable diaphragm) and allowing'the discharge of the excess pressure from heat exchange apparatus 11 through line 24.

While the invention has been described as'applied to a' heat exchange apparatus for the generation of steam using molten sodium heated by nuclear reaction, it is to be expressly understood that it is not limited thereto. The invention has application to any heat exchange apparatus wherein two fluids are passed in indirect heat exchange relationship and where one of the fluids is maintained at a pressure lower thanthe other fluid by means of a gas or vapor supplied to an expansion tank or pressurizer disposed in the low pressure side of the heat exchange apparatus.

It can be readily seen from the foregoing description that a pressure relief assembly for a heat exchange apparatus has been provided wherein a local rise in pres sure beyond the maximum safe pressure of the low' pressure side of the heat exchange apparatus is prevented. The invention also provides a pressure relief assembly wherein premature failure or leakage is greatly minimized since only the pressure relief device 23 is subject to differential pressure under normal operating conditions.

Although but one embodiment has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can .bemade .inv .the arrangement of parts without depart- 4 ing from the spirit and scope of the invention as the samewill now be understood by those skilled in the art.

What is claimed is:

1. In a fluid heat exchange system having a fluid heating means to provide a heated fluid, a heat exchanger communicating with said heating means to receive the heated fluid therefrom and a source of fluid to be heated at a pressure substantially greater than the pressure of the heated fluid, said heat exchanger being adapted to pass said heated fluid and fluid to be heated in indirect heat exchange relationship with each other, said heat exchanger being connected to deliver cooled heated fluid to said heating means for reheating, a pressnrizer having a vapor and liquid space, said pressurizer being in communication with said heat exchanger to receive heated fluid in said liquid space thereof and with a source of pressurizing fluid under pressure to receive pressurizing fluid in said vapor space to maintain the heated fluid under a relatively low pressure; the combination of a pressure safety assembly comprising, a first discharge conduit connected to communicate with the vapor space of the pressurizer and atmosphere, a first pressure relief .device in said conduit, said first pressure relief device being operative to prevent flow of pressurizing fluid through said conduit and to pass pressurizing fluid and heated fluid through said conduit when a pressure rise of the heated fluid causes a rise in pressure in the pres surizer above a maximum safe operating pressure, a second unobstructed discharge conduit connected at one end to the heat exchanger to receive heated fluid and at the other end connected to the pressurizer to receive pressurizing fluid from the vapor space of the pressurizer, and a second pressure relief device disposed in said second conduit in close proximity to said heat exchanger, said second pressure relief device being operative to pre vent flow of heated fluid through said conduit and to pass the heated fluid therethrough, before said first pressure relief device becomes operative to pass heated fluid through said first conduit, when the heated fluid attains a pressure value in the heat exchanger in excess of the maximum safe pressure of the assembly.

2. In the apparatus of claim 1 wherein said heated fluid and pressurizing. fluid are respectively molten sodium and a gas inert with respect to the molten sodium.

3. The apparatus of claim 1 wherein the first and second pressure relief devices are rupturable diaphragms.

4. The apparatus of claim 1 wherein the first and second pressure relief. devices are'spring loaded valves.

5. In a fluid heat exchange system having a fluid heating means to provide a heated fluid, a heat exchanger communicating with said. heating means to receive the heated fluid from the latter and with a source of fluid to be heated having a pressure substantially greater than the pressure of the heated fluid, said heat exchanger being constructed and arranged to pass said heated fluid and fluid to be heated in indirect heat exchange relationship with each other, said heat exchanger being connected to deliver cooled heated fluid to said heating means for reheating, a pressurizer communicating with said heat exchanger to receive heated fluid and connected to receive a pressurizing fluid under a relatively low pressure in the top thereof to maintain said heated fluid under a relatively low pressure, the combination of a pressure safety assembly comprising a first pressure relief device communicating with said pressurizer and operative to prevent flow of pressurizing fluid and heated fluid from the pressurizer and to pass pressurizing fluid and heated fluid from the pressurizer when a rise in the pressure of the heated fluid causes a rise in pressure in the pressurizer above the maximum safe operating pressure, a discharge conduit communicating with the heat'exchanger to receive heated fluid and at the opposite end with thepressurizer to receive pressurizing fluid, and a second pres-' sure relief device in said conduit operativeto prevent flow-of heatedfiuid andipressurizing fluidthrough said conduit and to pass heated fluid through the conduit before said first pressure relief device becomes operative to pass heated fluid and pressurizing fluid from the pressurizer when the pressure of the heated fluid attains a pressure value exceeding the maximum safe operating pressure of the system.

6. In a fluid heat exchange system having a fluid heating means to provide a heated fluid, a heat exchanger communicating with said heating means to receive the heated fluid therefrom and with a source of fluid to be heated at a pressure substantially greater than the pressure of the heated fluid, said heat exchanger being adapted to pass said heated fluid and fluid to be heated in indirect heat exchange relationship with each other, said heat exchanger being connected to deliver cooled heated fluid to said heating means for reheating, a pressurizer communicating with said heat exchanger and fluid heating means to receive heated fluid and connected to receive pressurizing fluid in the top portion thereof to maintain said heated fluid under a relatively low pressure; the combination of a pressure safety assembly comprising a first pressure relief device communicating with said pressurizer and operative to prevent flow of pressurizing fluid and heated fluid from the pressurizer and to pass pressurizing fluid and heated fluid from the pressurizer when a rise in the pressure of the heated fluid causes a rise in pressure in the pressurizer above the maximum safe operating pressure, an unobstructed discharge conduit connected at one end to the heat exchanger to receive said heated fluid under a relatively low pressure and at the opposite end to the pressurizer to receive pressurizing fluid therefrom, and a second pressure relief device disposed in said conduit in close proximity to said heat ex changer, said pressure relief device being operative to prevent passage of heated fluid through said conduit and to pass the heated fluid through the conduit before said first pressure relief device becomes operative to pass heated fluid and pressurizing fluid from the pressurizer when the heated fluid in the heat exchanger reaches a pressure value exceeding the maximum safe operating pressure of the system.

References Cited in the file of this patent UNITED STATES PATENTS 1,922,509 Thurm Aug. 15, 1933 2,360,665 Fields Oct. 17, 1944 2,645,906 Ryan July 21, 1953 2,690,056 Bergstrom Sept. 28, 1954 2,711,882 Narbutovskih June 28, 1955 FOREIGN PATENTS 1,141,588 France Mar. 18, 1957 UNITED STATES PATENT OFFICE CERTIFIGATION 0F CORRECTION Patent No 2 97l 746 February 14, 1961 Alan Bell U I d It is hereby certifiedthat error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 40, for "dnagerous" read dangerous line 41, for "appartus" read apparatus column 2, line 36, for "42" read 24 a,

Signed and sealed this 27th day of June 19610 (SEAL) Attest:

ERNEST W. SWIDEB. DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2.971,?46 February 1 1, 1961 Alan B611 It is hereby certified'that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 40, for "dnagerous" read dangerous g line 41, for "appartus" read apparatus column 2, 11ne 36, for 412" read 24 Signed and sealed this 27th day of June 1961c (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

